The synthesis of preferred polybenzimidazole based high performance fibers requires the selective polymerization of 2,3,5,6-tetraminotoluene (“TAT”) with various substituted and unsubstituted aromatic diacids, such as 2,5-dihydroxyterephthalic acid (“DHTA”).
TAT has been mentioned in the literature (e.g., U.S. Pat. Nos. 3,476,590 and 3,783,137) as a comonomer in the synthesis of polybenzarenazole polymers. TAT can be used as a crosslinking comonomer using radical induced crosslinking at the methyl group. For example, in Japanese Patent Application 2005-330470 A, TAT is used as a crosslinking comonomer in the synthesis of a polybenzimidazole polymer for film applications. However, none of these references discloses a source or synthesis for TAT.
There remains a need for a process for the safe and efficient production of high-purity 2,3,5,6-tetraminotoluene (TAT) and salts of 2,3,5,6-tetraminotoluene that can be converted to 2,3,5,6-tetraminotoluene, to make an aromatic diacid complex of 2,3,5,6-tetraminotoluene of high enough purity for use in making a high molecular weight polymer material for producing high-performance fibers. For reasons of cost and safety it would be highly desirable to have a process where intermediates do not need to be isolated as dry materials.